1. Field of the Invention
The present invention relates to an oscillator. More particularly, the present invention relates to an oscillator, a driving circuit and an oscillation method thereof, which can avoid loading noise of different frequency bands into a clock signal.
2. Description of Related Art
With development of technology, electronic products are continually innovated. Normal operation of the electronic product depends on an oscillator providing clocks. Based on the precise clock generated by the oscillator, internal chips of the electronic product can sequentially process received data or signals and transmit the processed data or signal to a next stage circuit at a correct time. A quartz oscillator can not only provide the precise clock, but also has a feature of not being influenced by factors such as temperature, humidity, fabrication process and operation voltage, etc. Therefore, the quartz oscillators are applied to most of the electronic products for providing the required clock.
FIG. 1 is a circuit diagram of a conventional oscillator. Referring to FIG. 1, the oscillator 100 includes a crystal 101, an inverter 102, a resistor R and a capacitor C. Since a mechanical-electrical resonance of the crystal 101 is quite stable, the oscillator 100 can output a relatively stable clock signal based on the above characteristic of the crystal 101. However, whether oscillation of the oscillator can be started is influenced by a quality of the crystal 101, and a waveform of a clock signal Xtal_out generated after the oscillation is also influenced by a quality of the crystal 101.
Generally, when a designer designs the oscillator 100, the quality of the crystal 101 cannot be known in advance. To eliminate a possibility that the oscillation of the oscillator 100 cannot be started due to a quality difference of the crystal 101, the inverter 102 with relatively great amplification is generally applied to the oscillator 100 for actuating the oscillation starting of the oscillator 100.
However, the inverter 102 with the relatively great amplification can also amplify amplitude of the clock signal Xtal_out generated after the oscillation starting of the crystal 101, which may lead to a full swing of the waveform thereof. Such full swing waveform is liable to be loaded with noises of different frequency bands, which can lead to instability of the waveform of the clock signal Xtal_out, and can influence a frequency of the clock signal Xtal_out.
For the oscillator, an optimal oscillation waveform is a sine waveform, which is not liable to be loaded with noises of different frequency bands, and the frequency of the provided clock signal is the most stable. However, for the oscillator applying the inverter with the relatively great amplification, due to the influence of the full swing waveform, if the quality of the utilized crystal is poor, the noises of different frequency bands generated by the crystal can be amplified, so that the waveform and frequency of the clock signal of the oscillator are influenced.